This application relates to thermoplastic resin/carbon fiber composites which have improved properties for use in electronic components.
Articles made from thermoplastic resins are commonly utilized in the material-handling devices, electronic devices and business equipment, for example chip carriers, and printer and copier components in contact with moving paper such as paper pathsxe2x80x94and moving components themselvesxe2x80x94such as ink-jet printer penholders. Electrostatic dissipation is an especially important issue within the electronic industry because of the inherently insulating nature of organic polymeric materials. Electrostatic dissipation (or discharge) is defined as a transfer of electrostatic charge between bodies at different potentials caused by direct contact or induced by an electrostatic field. As electronic devices become smaller and faster, their sensitivity to electrostatic dissipation (ESD) increases.
The US Department of Defense Handbook 263 (DOD-HDK-263) defines three categories of plastics for use in ESD protection: antistatic, static dissipating, and conductive. Characteristics of each type are listed in Table 1. Conductive fillers such as carbon fibers can be incorporated into polymeric materials to modify the electrical properties to achieve any of these three characteristics. In particular, carbon fibers facilitate dissipation of static charge and provide enhanced electromagnetic shielding. (See, for example, U.S. Pat. Nos. 4,559,164 and 5,004,561).
The present invention provides a carbon fiber-filled, thermoplastic resin composition which has improved electrical properties at a given level of carbon fibers. The compositions of the invention comprises thermoplastic resin and carbon fibers associated into bundles with a binder. The thermoplastic resin and the binder are selected to be incompatible such that the adhesion of the fiber to the resin is poor. In an embodiment of the invention, the composition comprises:
(a) a thermoplastic polymer selected from the group consisting of polystyrene, high impact polystyrene, polycarbonate, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyether imide and blends thereof; and
(b) carbon fibers associated into bundles with a polyamide terpolymer binder. The bundles are dispersed within the thermoplastic polymer.
The compositions of the invention can be used for injection molding of articles for use as components in applications requiring static dissipation and/or EMI shielding. Such articles include, but are not limited to electronic devices, dust handling equipment and notebook computer enclosures.